Mercury-Redstone

A modified version of the Redstone missile
used in NASA's initial effort to launch astronauts into space. In most respects,
the Mercury-Redstone was similar to its missile relative. In fact, the vehicle
was selected for the Mercury Project
because of its proven track record of safety and reliability. The Mercury-Redstone
incorporate additional safety features, as well as an upgraded Rocketdyne
engine. About 800 engineering changes were also made to the production version
of the Redstone to qualify it as a manned space launch vehicle. These included
extending the fuel tank by about 2 meters to increase the burn time and
thus achieve increased speed and altitude.

Alan Shepard, the first American astronaut,
was launched aboard a Mercury-Redstone from Cape
Canaveral Launch Pad 5 on May 5, 1961, on mission MR-3. A nearly identical
flight designated MR-4 carried Virgil Grissom
on Jul. 21, 1961. Mercury-Redstone mission performance in support of suborbital
manned flights MR-3 and MR-4 was so successful that two similar flights
which would have been designated MR-5 and MR-6 were cancelled.